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[2003:cb:c706:1700:6b81:27cb:c9e2:a09a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3730814602asm14910248f8f.44.2024.08.28.00.44.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 28 Aug 2024 00:44:05 -0700 (PDT) Message-ID: <9f9d7e96-b135-4830-b528-37418ae7bbfd@redhat.com> Date: Wed, 28 Aug 2024 09:44:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 06/19] mm/pagewalk: Check pfnmap for folio_walk_start() To: Peter Xu , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Gavin Shan , Catalin Marinas , x86@kernel.org, Ingo Molnar , Andrew Morton , Paolo Bonzini , Dave Hansen , Thomas Gleixner , Alistair Popple , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Sean Christopherson , Oscar Salvador , Jason Gunthorpe , Borislav Petkov , Zi Yan , Axel Rasmussen , Yan Zhao , Will Deacon , Kefeng Wang , Alex Williamson References: <20240826204353.2228736-1-peterx@redhat.com> <20240826204353.2228736-7-peterx@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240828_004411_959527_34793CC3 X-CRM114-Status: GOOD ( 25.98 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 26.08.24 22:43, Peter Xu wrote: > Teach folio_walk_start() to recognize special pmd/pud mappings, and fail > them properly as it means there's no folio backing them. > > Cc: David Hildenbrand > Signed-off-by: Peter Xu > --- > mm/pagewalk.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/pagewalk.c b/mm/pagewalk.c > index cd79fb3b89e5..12be5222d70e 100644 > --- a/mm/pagewalk.c > +++ b/mm/pagewalk.c > @@ -753,7 +753,7 @@ struct folio *folio_walk_start(struct folio_walk *fw, > fw->pudp = pudp; > fw->pud = pud; > > - if (!pud_present(pud) || pud_devmap(pud)) { > + if (!pud_present(pud) || pud_devmap(pud) || pud_special(pud)) { > spin_unlock(ptl); > goto not_found; > } else if (!pud_leaf(pud)) { > @@ -783,7 +783,7 @@ struct folio *folio_walk_start(struct folio_walk *fw, > fw->pmdp = pmdp; > fw->pmd = pmd; > > - if (pmd_none(pmd)) { > + if (pmd_none(pmd) || pmd_special(pmd)) { > spin_unlock(ptl); > goto not_found; > } else if (!pmd_leaf(pmd)) { As raised, this is not the right way to to it. You should follow what CONFIG_ARCH_HAS_PTE_SPECIAL and vm_normal_page() does. It's even spelled out in vm_normal_page_pmd() that at the time it was introduced there was no pmd_special(), so there was no way to handle that. diff --git a/mm/memory.c b/mm/memory.c index f0cf5d02b4740..272445e9db147 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -672,15 +672,29 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr, { unsigned long pfn = pmd_pfn(pmd); - /* - * There is no pmd_special() but there may be special pmds, e.g. - * in a direct-access (dax) mapping, so let's just replicate the - * !CONFIG_ARCH_HAS_PTE_SPECIAL case from vm_normal_page() here. - */ + if (IS_ENABLED(CONFIG_ARCH_HAS_PMD_SPECIAL)) { + if (likely(!pmd_special(pmd))) + goto check_pfn; + if (vma->vm_ops && vma->vm_ops->find_special_page) + return vma->vm_ops->find_special_page(vma, addr); + if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)) + return NULL; + if (is_huge_zero_pmd(pmd)) + return NULL; + if (pmd_devmap(pmd)) + /* See vm_normal_page() */ + return NULL; + return NULL; + } + + /* !CONFIG_ARCH_HAS_PMD_SPECIAL case follows: */ + if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) { if (vma->vm_flags & VM_MIXEDMAP) { if (!pfn_valid(pfn)) return NULL; + if (is_huge_zero_pmd(pmd)) + return NULL; goto out; } else { unsigned long off; @@ -692,6 +706,11 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr, } } + /* + * For historical reasons, these might not have pmd_special() set, + * so we'll check them manually, in contrast to vm_normal_page(). + */ +check_pfn: if (pmd_devmap(pmd)) return NULL; if (is_huge_zero_pmd(pmd)) We should then look into mapping huge zeropages also with pmd_special. pmd_devmap we'll leave alone until removed. But that's indeoendent of your series. I wonder if CONFIG_ARCH_HAS_PTE_SPECIAL is sufficient and we don't need additional CONFIG_ARCH_HAS_PMD_SPECIAL. As I said, if you need someone to add vm_normal_page_pud(), I can handle that. -- Cheers, David / dhildenb